Production of tubular rivets and similar articles



Jan. 22, 1952 E. H. LYNALL PRODUCTION OF TUBULAR RIVETS AND SIMILAR ARTICLES Filed Sept. 22, 1947 2 SHEET. SHEET l Attorney E. H. LYNALL Jan. 22,1952

PRODUCTION OF TUBULAR RIVETS AND SIMILAR ARTICLES 2 SHEETS-SHEET 2 Filed Sept. 22, 1947 FIGS.

Iii/a 2 I nventor I Attorney Patented Jan. 22, 1952 PRODUCTION OF TUBULAR RIVETS AND SIMILAR ARTICLES Ezra Herbert Lynall, Four Oakes, England Application September 22, 1947, Serial No. 775,510 InGreat Britain August 18, 194 7 Claims.

This invention relates to the production of tubular metal rivets and is especially applicable to the production of a so-called blind rivet having its shank portion made of constant outside diameter, with a stepped bore made by forming a counterbore in one end of the bore so as to reduce the diameter of the bore at one end of the shank to increase the wall thickness of the shank at that portion and thus permit of internal screwthreading in the thick walled portion, said blank being provided with a head-forming flange around the mouth of the counterbore. A blind tubular rivet of this character is adapted to be installed by inserting the tubular shank of the rivet into aligned holes in two or more plate portions to be riveted so that the head-forming flange of the rivet lies upon the face of one of the plates, holding the head against movement and simultaneously applying axially a steady force or a single sharp blow or a series of percussions, e. g. by means of a push-rod or of a pull-rod engaged with the screw-threaded portion of the bore or by means of an equivalent mandrel-like member. so as to cause the thin-walled portion of the shank to collapse by outward bulging in order to form a flange opposed to the rivet head, the plates being held between said head and flange.

The main object of the present invention is to provide improved methods of producing a tubular metal rivet of the above character from long lengths of tubing.

A further object of the invention is to provide improved methods of and apparatus for cold forging a rivet blank having a flanged head and a stepped bore from a short length of straight tub ing having a uniform wall thickness. t

In order that the invention may be more.readily understood a method of and apparatusifor. producing a tubular flanged rivet with a stepped bore from seamless metal tubing will now be .described with the aid of the accompanying drawings, wherein:

Figure 1 is a sectional view of the die and the preforming punch at the commencement of the preforming operation,

Figure 2 is a sectional view of the die and the preforming punch at the termination of the preforming operation,

Figure 3 is a sectional view of the partly formed rivet as it appears after the preforming operation.

Figure 4 is a sectional view of the rivet as it appears after the finish forging operation,

Figure 5 is a sectional view of the punch employed in the finish forging operation, and

Figures 6, 7, 8 and 9 die and the finishing punch at various stages of the finish forging operation.

Figures 1 and 2 showing the preiorming operation are drawn to a larger scale than Figures 6,

7, 8 and 9 showing the finish forging operation.

Figure 5 is drawn to a larger scale than thatused for Figures 1 and 2 and Figures 3 and 4 are drawn to the same scale which is larger than that used in any other figure. 1

The tubular rivet illustrated in Figure 4 of the accompanying drawings. is complete except for the forming of a female screwthread in the thickened wall of the rivet and for its production short blanks are parted-01f from seamless; tube made of any suitable malleable or deform-- able material, such as a heat-:treated aluminum alloy, the blanks being barrelled or otherwise dressed to remove any burrs formed by the-cutting saw and one such straight tubular blank 1 of constant outside diameter and uniform wall thickness is inserted in the cavity 2 in the die 3 of a rivet heading machine, as shown in Figure l. Theblank l is a snug fit within the die cavity 2.

the inner end of which is provided by the end face of an ejector 4. The ejector 4 is arranged so that part of the blank I projects out from the die cavity 2 and-the position of the ejector 4 is adjusted between the two successive heading operations to which the blank I is subjected.

The first heading operation is for preforming purposes and is effected by means of a tapered spigot punch 5 which projects from the end face of a Y solid punch body 6, a flange-bending die cavity I surrounding the root end of the spigot punch 5. In a single stroke this first punch, by means of the first heading or preforming operation the blank I has the shape shown in Figure 3, that is, with a partly formed counterbore I in the mouth of the blank I at the end thereof having the preformed head flange I. The diameter of the outside surface I and the original bore i beyond the partly formed counterbore I remain unchanged as the result of the-preforming operaj tion, there being a rough shelfflf, formed between said partly formed counterbore 1 and the unchanged length of bore I. in order to ensure turning over of the end of thestraight blank to are sectional views of the form the head flange I a generous radius has to be provided at the junction between the spigot punch and the die cavity 1 and this is reproduced in the preformed blank as indicated at i in Figure 3. If desired, the second heading or finish forging operation may be effected after the blank has been transferred to another die in another machine or in the same machine, but for preference the finishing operation is carried out while the partly formed blank is held in the same die cavity as that in which it is held during the preforming operation.

For purposes of economical production, ,however, the rivet heading machine would be run for preforming a batch of blanks before any rivet is finished forged.

At the end of the preforming stroke 'of the machine the opposed faces of the die 3 and of the punch body 6 are in abutment so that the preformed flange I is confined within a closed space. The ejector 4of the die 3, assuming the same dieis used for the finishing operation, is accordingly adjusted prior to the finish forging operation, in order to decrease the length of the die cavity 2, so that when the preformed blank I is re-inserted therein its head end projects beyond the face of the die 3 so as to space the head flange I therefrom, as shown in Figure 6. The re-inserted blank I is forced back hard against the ejector 4 by the punch assembly used for the finishing operation.

The finishing punch assembly is shown in Figure 5 and comprises a hollow punch body 8 having a bored nose '9 'within which is telescopically slidable the sleeve-like forward end I!) of a hollow ram II. The head I2 of the ram II is accommodated within a' space formed within the hollow nose 9 andat the end of a hollow externally screwthreaded base It which is mounted on the punch-holding slide I l of the rivet heading machine. The body 8 is screwed on to the base I3 and is locked in position by the nut I5. Centrally within the base I3 and body 8 is a mandrel I6 which is attached to the base I3 by a screwed connection so that the mandrel It can be axially adjusted in relation to the base I3 and to the adjustable body 8 and secured in the ad usted position by a locknut IT. The forward end of the mandrel IE is formed with a pilot I8 and is slidably accommodated within the bore of the sleeve III and head I2 of the telescopic ram II. A coiled compression spring I9 encircles the mandrel I6 and is interposed between the head end 20 of the base I3 and the top of the ram head I2 so as normally to project the sleeve II! of the ram I I as far out of the nose 9 as possible. It will be readily understood that the mandrel I6 is fixed relatively to the body 8 and that the ram II telescopes between the inner mandrel I6 and the outer body 8.

While the punch assembly is approaching the operative position there is no relative movement between the components thereof, the resistance of the spring I9 being sufficient, on the ram sleeve I0 contacting with the head flange I of the preformed blank I, to force the blank I hard down upon the ejector 4. During the period of sustained axial pressure which follows the foreing home of the blank I hard on to the ejector 4 the stifiness of the blank I is sufficient to overcome the opposition of the spring IS with the result that the telescopic ram sleeve I I1 is forced back until it seats solidly against the end of the base I3. Before this position has been reached the mandrel I6 has entered into the preformed 4 counterbore I of the blank I and by the time the ram I I has reached the position in which it is arrested by the base I3, as shown in Figure '7, the pilot I8 of the mandrel I6 has partly entered a socket 2| in the ejector 4, the conical neck 22 between the mandrel I8 and its pilot I8 has contacted with the shelf I (see Figure 3) in the blank ;I and the end face of the ram sleeve .II has retreated into the bore of the body nose 9 sumciently to form around the mandrel IS an annular space within which the preformed flange I is accommodated. As the ram II cannot retreat any further into the punch body 8, the ram H, the punch body 8, and the mandrel It continue to advance in unison for the final stage of the finishing operation, until the nose 9 of the punch body -8 contacts with the face of the die 3 and thus constitutes a closed cavity within which the head flange I of the blank I is trapped, as shown in Figure 8. One result of this final stage in the finishing operation is that the generous radius .I made on the blank I in the preforming operation disappears, leaving the mouth of the counterbore I (Figure 4) with a sharp corner I The other result of this final stage in the finishing operation is that the act of forcing the blank I into the die cavity 2 causes the metal displaced by the axial pressure of the punch assembly to shrink around the uncovered portion of the pilot I8, the diameter of which On completion of the operating stroke the punch base I3, the mandrel I6 and the punch body 8 withdraw, leaving the ram II projected (see Figure 9) under the action of its spring I9 so as to extract the mandrel I6 from the finished blank without lifting the latter from the die cavity 2. When the whole punch assembly has eventually risen clear of the die 3 the ejector 4 is operated in known manner to expel the finished blank. The ejected rivet having the form shown in Figure 4 requires little or no finishing apart from tapping of the screwthread I (indicated in dotted lines) in the small diameter portion I of the bore, by any suitable method and means.

It will be readily appreciated that by appropriately adjusting the punch body 8 and the mandrel I6 in relation to the punch base I3 the amount of retreat A of the ram II within the body 8 may be varied to forge head flanges of different thicknesses.

I claim:

1. A method of cold forging by means of a rivet heading machine a tubular rivet having an said preforming operation consisting in initially forming the flanged head by pressure applied axially by means of a first punch and said finishing operation consisting in forming the bore of the tubular blank by pressure applied axially by a second punch which upsets inwardly part of the metal formingthe interior of said blank to cause it to shrink onto a stepped mandrel carried by said second. punch, said stepped mandrel having one part with an external diameter 6 approximately the, same size as the uniform bore of the blank, and another part with an external diameter appreciably smaller in size than the uniform bore of the blank, said blank bein accommodated snugly during the preforming operation and during the finishing operation within a die cavity which restrains the blank against any appreciable swelling.

2. A method of machine forging a flangedhead tubular rivet or similar metal article having a shank with a non-uniform bore from a tubular blank havinga bore of substantially uniform diameter throughout, comprising a preforming operation and a finishing operation performedon the said tubular blank, said preforming opertion consisting of initially forming a head flange on one end of said blank, by pressure applied axially by a first punch, and said finishing operation consisting in forming the bore of the blank by pressure applied axially by asecond punch which internally upsets part of the metal forming said blank to cause it to shrink onto a mandrel carried by said second punch and accommodated snugly during both operations within a die cavity which restrains the blank against any appreciable swelling.

3. A method as claimed in claim 2 characterized in that the preforming and finishing operations are effected in succession without removing the tubular blank from its shape-conserving cavity in the blank-holding die.

4. A method of cold forging by means of a rivet heading machine a tubular rivet having an external head flange at one end only of a shank of plain cylindrical external form provided with a stepped bore formed by making a thickened wall portion of substantial length at the unflangd end of the shank from a tubular blank in the form of an unflanged cylindrical shell of substantially uniform bore and wall thickness, comprising a preforming operation and a finishing operation performed in succession while the tubular blank is accommodated snugly within a die cavity which restrains the blank against any appreciable swelling, said preforming operation consisting of applying axial pressure by a flrstpunch for initially forming the head flange and for initially modifying the bore by displacement toward the unflanged end of said blank of metal from the mouth of the head end of said blank, and said finishing operation consisting in finish forming said bore by applying axial pressure by a second punch which upsets inwardly part of the metal forming the interior of the blank to cause it to shrink onto a stepped mandrel carried by said second punch, said stepped mandrel having one part with an external diameter approximately the same size as the uniform bore of the blank, and another part with an external diameter appreciably smaller in size than the uniform bore of the blank, and in finish forming the head flange in a cavity formed between said blank-holding die and said second punch.

5. A method as claimed in claim 4, wherein a generous corner radius is formed in the mouth of the bore at the head end of the tubular blank in the preforming operation and the mouth radius is reduced so as to provide a substantially sharp corner in the following finishing operation.

6, A method of cold forging by means of a rivet heading machine a tubular rivet having an external head flange at one end only of; a shank of plain cylindrical external form provided with a stepped bore formed by making a thickened wall portion of substantial length at the unflanged end of the shank from atubular blank in the form of an unflanged cylindrical shell of substantially uniform bore and wall thickness having one part with an external diameter ap-' proximately the same size as the uniform bore of the blank, and another part with an external 7 diameter appreciably smaller in size than the uniform bore of the blank. a

7. Apparatus for cold forging a tubular rivet having an external head-flange at one end only of a shank of plain cylindrical external form provided with a stepped bore formedby makinga thickened wall portion of substantial length at the ,unflanged end of the shank from a tubular blank in the form of an unflanged cylindrical shell of substantially uniform bore and wall thickness, comprising a frame, a die fixed on said frame and having a cavity adapted to receive snugly the tubular blank and a co-operating punch movable on said frame relative to said die and comprising a punch body, a hollow ram telescopically slidable within said punch body and adapted to apply pressure on the head end of the blank in the direction of the longitudinal axis, and a mandrel over which said hollow ram slides, said mandrel being fixed within said punch body and axially adjustable in relation to the punch body for determining the depth of said counterbore and adapted to apply axial pressure in the same direction as the ram to upset inwardly part of the metal of the interior of the blank to cause it to shrink on to said mandrel which has an external stepped shape corresponding to that required in the bore of the finished article, namely one part with an external diameter approximately the same size as the uniform I bore of the blank and another part with an external diameter appreciably smaller in size than the uniform bore of the blank, said ram being adapted to telescope into the punch body surficiently to constitute within the mouth of the bore of said punch body in which said ram slides and around said mandrel a cavity definingthe overall diameter and the thickness of the finished flanged head of the tubular blank, said punch cavity being closed by abutment against a face of the blank-holding die.

8. Apparatus for cold-,forging a tubular rivet having an external head flange at one end only of a shank of plain cylindrical external form provided with a stepped bore formed by making a thickened wall portion of substantial length at the unflanged end of the shank, from a tubular-blank in the form of an unfianged cylindrical shell of substantially uniform bore and wall thickness, comprising a frame, a die fixed to i said frame and having a cavity adapted to receive snugly the tubular blank and first and second punch means movable on said frame for cooperating with said die in succession, said first punch means being adapted to preform a head flange on one end of said blank and to preform the counter-bore by means of a spigot punch and a surrounding bending die cavity, and said second punch means consisting of a punch body, a hollow ram telescopically slidable within said punch body and adapted to apply pressure on themthe head end or the blank an "the nir'ection of the longitndinal axis, a stepped mandrel fixedwithin said punch bodly so as to guide said hollow ram which slides over :said mandrel, :said -:maz 1drel having one part with an external diameter approximately the -sairiie size as the uniform bore of the blank and another ,part with an external diameter appreciably smaller in size than the uniform bore of the :blank and being adapted. to apply axial pressure the same direction as the ram to upset inwardly part of the metal of the interior of the blank to cause it to shrink onto said mandrel, said ram and mandrel combining with the punch body and die to constitute a :closed cavity which produces the final form of the flanged head of the blank.

9. Apparatus as claimed in claim '8 characterised iii-that thefram =of =saidseoond punch means is adapted to telescope into the punch bodyagainst spring resistance sufficiently to constitute within the mouth of the bore 01" said punch body in which said ram slides and around said -mandz el a cavity defining the overall diameter and the thickness of the finished flanged head of the tubular blank, said punch cavity being closed by abutment against a face of the blank-holdmg die.

v 8 :10. apparatus as maimed 1h Ialm 8, characterised in that fithe mandr'el or said second punch means, :15 axially adjustable in relation to the punch body for the purpose of determining thedepth from the end faoe of the head end of the blank 0f the counte'r-bor'e which results in "the formation of the stepped bore.

1,214,070 Pr'o'ske he; Jan. 30, 1917 1,618,446 Kuhne Feb. 22, 1927 1,718,630 Brown a- June 25, 1929 1,900,572 Lyman 1-- Mar. 7, 1933 2,040,939 Huck May 19, 1936 2,045,629 Huck e Sept. 15, 1936 2,436,185 'Torresen l Feb. 17, 1948 

